Promise deferred

promise_deferred.js

function getSomeJSON(url, callback) {
  // AJAX call to get data from server. Accepts callback and calls
  // with callback(err, response)
  ...
}
  
function fetchJSON(url) {
  var deferred = new Deferred();
  getSomeJSON(url, function (err, response) {
    if (err) return deferred.reject(err);
    deferred.resolve(response);
  });
  return deferred.promise;
}
  
fetchJSON("http://www.google.com").then(..);